1. Field of the Invention
The present invention relates to an improved flexible bearing and to an improved method of making flexible bearings.
2. Description of the Prior Art
It is known in the prior art to utilize in flexible bearings a lamination comprised of alternate layers of an elastomeric material and rigid reinforcement shims that are stacked and bonded together. With elastomer as both the top and bottom layers, the lamination is positioned between and bonded to metallic end rings. One end ring may comprise the thrust-nozzle ring of a rocket motor and the other the rocket case mounting ring. The lamination is characterized in that it is flexible in directions parallel to the layers, but is relatively unyielding in directions perpendicular thereto.
This type of flexible bearing has many uses in addition to mounting a movable thrust nozzle to a rocket motor case including applications to motor mounts and bridge abutments. In its application to mounting a movable thrust nozzle to a rocket motor case, the flexible bearing is annular in form. Additionally, the layers of elastomer and the rigid reinforcement shims are shaped to conform to the surfaces of concentric spheres thereby to enable the thrust nozzle to be rotated about a fixed point. This is desirable for precision control of the rocket.
A typical bearing of this type having practical application for mounting a movable thrust nozzle to a rocket motor case is disclosed in U.S. Pat. No. 3,941,433 issued on Mar. 2, 1976 to William T. Dolling et al., and assigned to the assignee of the present invention.
In U.S. Pat. No. 3,941,433 a preferred material for the rigid reinforcement shims is said to be a hightemperature steel. Reinforcement shims made of materials other than steel are also known. Thus, reinforcement shims have been fabricated from non-metallic materials such, for example, as glass cloth. Such reinforcement shims contain, in addition to the cloth, a resin or hardening material.
In the fabrication of such reinforcement shims from non-metallic materials for mounting a movable thrust nozzle to a rocket motor case, it has been the practice in the prior art to separately prefabricate, in cured form, each of the plurality of rigid reinforcement shims that are employed in the flexible bearing lamination. An individually associated mold has been required for each of the reinforcement shims because each reinforcement shim conforms to the surface of an individually associated sphere having its own, unique radius. Thus, in a lamination having nine reinforcement shims in the stack, for example, nine separate and different molds are required for the prefabrication of the shims.
This prior art practice involving a multiplicity of molds for the lamination of each flexible bearing being fabricated not only significantly and undesirably adds to the cost of the necessary tooling, but also is labor intensive. Such tooling and labor costs escalate and become particularly onerous where fabrication of flexible bearings of several different sizes is involved. This is because of the numerous molds required to be used and the necessity for guarding against mixup of the many prefabricated reinforcement shims being produced. Additionally, the rejection rate of laminations made from prefabricated rigid reinforcement shims has been undesirably high. As a result, it has been necessary to conduct a very thorough inspection of each prefabricated reinforcement shim for the flexible bearing lamination to determine if it is in conformance with the required standards for the specific use for which fabricated. This has significantly added further to the labor cost.
Thus, there exists a need and a demand in the art for improvement in flexible bearings and the method of making the same to the end of eliminating, or at least, reducing costly tooling and labor in the prefabrication of the reinforcement shims, and also in substantially reducing the rejection rate of finished bearings. The present invention was devised to fill the technological gap that has existed in the art in these respects.